My question involves chassis grounding to earth ground.
My PCB circuit is a simple signal generator using a microcontroller. It has a separate 'ground' from earth ground, supplied by a floating 5VDC source. (I guess we would call this a digital ground?)
The PCB is to be installed inside a metal chassis (aluminum, I believe). Inside, there is a 15VDC converter. As a signal generator, it outputs a signal with reference to the +5V.
Unfortunately, the device that uses this output signal is grounded to the earth ground, not the digital ground.
The signal, which is supposed to drive a motor, ends up having severe noise problems.
What I found out was that if I provide the chassis (not the circuit ground) a capacitative ground to the earth ground by connecting a capacitor from the chassis to the earth ground pin, the noise problem disappears. However, if I connect the earth ground DIRECTLY to the chassis, the circuit is shorted.
So my question would be, is it normal/safe to ground the chassis of a circuit with digital ground using only a capacitor? If not, is there a better way to fix the noise issue?
Also, even with the capacitor to the earth ground, whenever a large machinery sharing the same earth ground turns on, my device shorts for an instant, and resets the microcontroller. Is this caused by a large current draw from the big machinery? But how so, if only the earth ground is common?